Virtualization - May 2023 - [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression

On 05/24, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg at redhat.com> writes:
>
> > Yes, but probably SIGABRT/exit doesn't really differ from SIGKILL
wrt
> > vhost_worker().
>
> Actually I think it reveals that exiting with SIGABRT will cause
> a deadlock.
>
> coredump_wait will wait for all of the threads to reach
> coredump_task_exit.  Meanwhile vhost_worker is waiting for
> all of the other threads to reach exit_files to close their
> file descriptors.
Indeed, I didn't think about this.


So why do we actually need CLONE_THREAD ? Can't vhost_worker() be a kernel
thread?

kthread_create() won't be convenient, but how about kernel_thread() ? it
inherits
mm/cgroups/rlimits/etc, kthread_stop() should work just fine.

Oleg.

Oleg Nesterov <oleg at redhat.com> writes:
> On 05/24, Eric W. Biederman wrote:
>>
>> Oleg Nesterov <oleg at redhat.com> writes:
>>
>> > Yes, but probably SIGABRT/exit doesn't really differ from
SIGKILL wrt
>> > vhost_worker().
>>
>> Actually I think it reveals that exiting with SIGABRT will cause
>> a deadlock.
>>
>> coredump_wait will wait for all of the threads to reach
>> coredump_task_exit.  Meanwhile vhost_worker is waiting for
>> all of the other threads to reach exit_files to close their
>> file descriptors.
>
> Indeed, I didn't think about this.
>
>
> So why do we actually need CLONE_THREAD ? Can't vhost_worker() be a
kernel thread?
>
> kthread_create() won't be convenient, but how about kernel_thread() ?
it inherits
> mm/cgroups/rlimits/etc, kthread_stop() should work just fine.
Basically with no patches that is where Linus's kernel is.

User complained about the new thread showing up in ps.  So the
exploration of how we could use CLONE_THREAD instead of what is
currently merged began.

Eric